Method for the manufacture of mineral wool products

ABSTRACT

A method for the manufacture of mineral wool products is disclosed. In one example, the method comprises reacting an aqueous phenol-formaldehyde resole with free formaldehyde with a first amount of urea, thereby preparing a prereact. The prereact is contacted with a second amount of urea. The resulting mixture of prereact and second amount of urea, as part of a binder, optionally with additives is applied to the surface of mineral fibers. The binder is cured on the surface of the mineral fibers. A mineral wool product with reduced emissions of formaldehyde is also disclosed.

FIELD OF THE INVENTION

The present invention relates to a method for manufacturing mineral woolproducts with binders based on phenol-formaldehyde resoles. The mineralwool products obtained are primary intended to be used as thermal andacoustic insulation of objects such as buildings, transportation,air-conducting ducts and appliances.

BACKGROUND

Mineral wool products are widely used for the thermal and acousticinsulation of different parts of buildings, transportations, orappliances, as well as for fire protection. Mineral wool materials aremainly randomly interlaced masses of mineral fibers with varying lengthsand usually bound by a cured resin-based binder. Three types of mineralmaterials are most commonly employed, glass, stone or slag. Processesfor the production of mineral wool products are well known in the art,and usually comprise the steps of melting the mineral material to anadequate temperature, fiberizing the molten mixture into fine fibers,application (mainly spraying) of an uncured liquid binder composition tothe individual fibers while they still have some residual heat,collection of the fibers and formation of a primary fleece on aforaminous conveyor, densifying the fleece, and curing the binder atelevated temperatures. The cured mat is then cut to the desired sizewith transverse and edge trimmers, before it is packaged for transport.

The most extensively used binders are based on thermosetting aqueousphenol-formaldehyde resoles, due to their good performance andattractive low cost. Most common phenol-formaldehyde resoles used forthis purpose are manufactured by phenol methylolation with formaldehydeand partial condensation in aqueous solution, catalyzed by strongalkaline substances. A detailed description of the preparation andcharacteristics of phenol-formaldehyde resoles suitable to be used inbinders for mineral wool can be found for instance in ‘Phenolic Resins:A Century of Progress’, chapter 10, edited by L. Pilato and published bySpringer-Verlag in 2010.

Phenol-formaldehyde resoles for mineral wool production arecharacterized by being prepared with a stoichiometric excess offormaldehyde, which results in free, unreacted, formaldehyde being mixedwith the resole reaction product. In the recent years, there has been anincreasing concern about the toxicity of formaldehyde, and formaldehydecontaining materials, which has led to the development of approaches tocope with this concern.

In this respect, urea has been found highly useful, so much that it isnowadays mostly always added to the resoles used for mineral woolmanufacture. Urea plays a dual role: first, it acts as a formaldehydescavenger, reacting with the free formaldehyde in the resole and thuslowering its concentration; and second, it works as a resin extender,being incorporated into the cured thermoset binder without deterioratingunacceptably its properties, and thus increasing the usable solidcontent of the binder at low cost. Urea extension levels commonly usedrange from 20-40 wt. %, depending on the starting resole, relative tothe sum of the dry weight content of the resole and the weight of urea.Higher levels of urea extension, if no countermeasures are adopted, havebeen reported to result in reduced binder mechanical properties,particularly after ageing, together with the production of high ammoniaemissions and the formation of troublesome “blue smoke” during mineralwool manufacture.

Urea might be added to the phenol-formaldehyde resole as soon as thereaction between phenol and formaldehyde is quenched. The resole andurea mixture is then allowed to react, usually at temperatures up to 60°C. and for up to 24 h. The industry often refers to this process as“premixing” or “prereacting”, and the phenol-formaldehyde-urea productobtained is called “premix” or “prereact”. The prereact is then storedand transported before use. There are known drawbacks associated withthe application of the urea prereact method; the prereact isconsiderably less stable than the phenol-formaldehyde resole (the higherthe ratio of urea, the less stable), what turns into much shorter usablestorage times. Furthermore, temperatures <10° C. need to be avoided forthe prereact.

To address the stability problems, urea might alternatively be added tothe phenol-formaldehyde resole by the mineral wool manufacturer at itsproduction site, shortly before the mixture is applied to the mineralfibers. Prolonged storage or transport of the prereact is therefore nolonger needed. In this case, the industry sometimes refers to urea being“cold” added, to distinguish it from the prereact formation (in theprereact method, urea is frequently added to the resole reaction productwhen it is still warm). Cold urea addition has however also itsdisadvantages. For instance, the presence of unreacted urea, which hadnot sufficient time to react, has been associated with increasedundesired emissions of ammonia and amines during mineral woolmanufacture. Furthermore, when urea is first added just shortly prior toapplication to the fibers, resoles with high content of freeformaldehyde need to be stored, transported and handled with theassociated concerns related to their toxicity.

The combination of both prereacting and cold urea addition has beendescribed, e.g. in patent publications U.S. Pat. Nos. 5,538,761 A1,5,670,585 A1 and US 2007191574 A1. However, the disclosed content offree formaldehyde in the starting resoles expressed with respect to awet weight instead of with respect to a dry weight, evidences that thedisclosed starting resoles require a high content of free formaldehyde.

Although the use of urea has been helpful reducing the concerns relatedto the free formaldehyde content in the phenol-formaldehyde resole basedbinders, it has not been totally satisfactory regarding emissions offormaldehyde from the manufactured mineral wool products. This is due tothe fact that urea-formaldehyde reaction products have been proved notto be sufficiently heat stable, and during curing at temperatures higherthan 100° C., they give back formaldehyde which is released from theproduced mineral wool products.

Reducing the emissions of formaldehyde from mineral wool products hasbeen extensively researched. Most approaches entail the use offormaldehyde scavengers other than urea to trap irreversibly the excessof formaldehyde, like melamine, dicyandiamide, alkanolamines, glycine,and substances with active methylene groups, among others. This approachhas however significant drawbacks. The most important ones are the extracost of the scavengers used, and the need for extra processing steps andinstallations. Additionally the scavengers might detrimentally affectthe resin stability and processability.

The inventors noticed that there is a need in the field for an improvedmethod for the manufacture of mineral wool products with a binder basedon phenol-formaldehyde resoles, which avoids storing, transporting, andhandling materials having high free formaldehyde content, and whichresults in mineral wool products with reduced formaldehyde emissions,without having to employ formaldehyde scavengers different than urea.

DESCRIPTION OF THE INVENTION

In view of the above, the inventors have developed an alternative methodwhich results in combination of a number of important advantages both inthe manufacture of mineral wool products and in the products themselves,advantages which are surprising and unanticipated by the prior art.

According to the invention, the method comprises a first step ofproviding an aqueous phenol-formaldehyde resole having free formaldehyde(step a)). In other words, the method envisages providing the aqueousproduct of methylolation and condensation of a phenolic compound withformaldehyde in alkaline conditions, wherein the formaldehyde is inmolar stoichiometric excess in relation to the phenolic compound, sothat after reaction, excess of free, unreacted, formaldehyde remainsmixed with the reaction product.

Advantageously, aqueous phenol-formaldehyde resoles with low freeformaldehyde content, i.e. with free formaldehyde content of 10 wt. % orless in relation to the dry weight content of the resole, can be used inthe method of the invention without compromising the stability of theresulting products. Thus, in preferred embodiments, the aqueousphenol-formaldehyde resole in this step a) has a free formaldehydecontent of 10 wt. % or less, preferably of 6 wt. % or less, and alsopreferably of at least 1 wt. %, in relation to the dry weight content ofthe resole, when measured according to the method ISO 9397:1995(hydroxylamine hydrochloride method).

In a subsequent step (step b)), the method foresees preparing aphenol-formaldehyde-urea prereact by contacting the phenol-formaldehyderesole with a first amount of urea (U1), and allowing the resole andurea mixture to react. When urea is contacted with thephenol-formaldehyde resole having free formaldehyde in a so-called“premixing” step, and among other occurring reactions, urea reacts withthe free formaldehyde by the methylolation of urea. As a result, thecontent of free formaldehyde in the resole is abruptly reduced with theamount of urea used. By phenol-formaldehyde-urea prereact it is meantthe reaction product mixture formed when urea is contacted with theresole and after the mixture has being allowed to react for sufficienttime and at sufficient temperature as to have caused the abruptreduction of free formaldehyde content. It should be understood thatreactions might still continue in the formed prereact after theformaldehyde content has reached a lower plateau, however, at a muchlower rate.

In preferred embodiments, the phenol-formaldehyde resole and urea areallowed to react for at least 1 hour, preferably at a temperaturebetween 10-60° C., to prepare the phenol-formaldehyde-urea prereact instep b).

The phenol-formaldehyde-urea prereact prepared according to thepreferred embodiments is stable for at least several days, and even forat least several weeks. This time allows the transport of the prereact,e.g. from the resole producer to the mineral wool manufacturer, and itsstorage prior to use as part of the mineral wool binder. By stable it ismeant that the prereact does not suffer relevant deterioration of itsproperties, which are required for the application as part of a binderin the manufacture of mineral wool. Some of the properties of theprereact which are maintained during days or weeks are sufficient lowviscosity, enough water dilutability, absence of precipitates and/oradequate B-stage gel-time.

In a subsequent step (step c)) of the method according to the invention,the phenol-formaldehyde-urea prereact formed in step b), is contactedwith a second amount of urea (U2). It should be understood that thisstep is done separately from step b), this is, from the preparation ofthe prereact referred to in the previous paragraphs. In preferredembodiments, the second amount of urea (U2) is added to the prereact atleast 24 h after the prereact has been formed, preferably at least 72 h.This subsequent step c) is advantageously done shortly before themixture is applied to the surface of mineral fibers in the manufactureof mineral wool products, preferably less than 48 h before, and morepreferably less than 24 h before.

The resulting phenol-formaldehyde-urea prereact and urea mixture fromstep c) is then applied to the surface of mineral fibers in a subsequentstep d), according to the method of the invention. The mixture isapplied as part of an aqueous binder optionally comprising at least oneadditive selected from curing catalysts (e.g. ammonium sulfate), resinextenders different than urea (e.g. carbohydrates), anti-dust agents(e.g. mineral oil), adhesion promoters (e.g. silanes) andwater-repellent agents (e.g. silicones). Preferably, the bindercomprises optional additives in a concentration of 1-30 wt. % related tothe non-aqueous content of the binder. According to certain embodiments,the addition of a resin apart from the aqueous phenol-formaldehyderesole of step a) is excluded.

In certain embodiments, in step d) the phenol-formaldehyde-urea prereactand urea mixture from step c) is applied to the surface of the fibers aspart of an aqueous binder with a non-aqueous content in the range 4-15wt. % relative to the weight of the aqueous binder, preferably in therange 6-13 wt. %, even more preferably 8-10 wt. %.

Preferably, the phenol-formaldehyde-urea prereact and urea mixture and,therefore the binder, is applied by spraying onto the surface of freshlyformed fibers arising from a fiberizing device.

The phenol-formaldehyde-urea prereact and urea mixture applied as partof the binder to the fibers is then cured in a subsequent step (step e))in the method according to the invention.

In preferred embodiments, the phenol-formaldehyde-urea prereact and ureamixture is cured by passing the mineral fibers bearing it through anair-circulated curing oven set at temperatures above 100° C., preferablyat a temperature between 140-180° C. The curing time preferably rangesfrom 3-5 minutes.

According to the invention, the method is further characterized by thefeatures:

(i) the total amount of urea (Ut) is between 30 and 35 wt. % relative tothe sum of the dry weight content of the phenol-formaldehyde resole andthe total amount of urea (Ut), and the second amount of urea (U2) usedin c) is between 20-35 wt. % of the total amount of urea (Ut); or(ii) the total amount of urea (Ut) is about 40 wt. % relative to the sumof the dry weight content of the phenol-formaldehyde resole and thetotal amount of urea (Ut), and the second amount of urea (U2) used in c)is about 25 wt. % of the total amount of urea; or(iii) the total amount of urea (Ut) is between 42 and 50 wt. % relativeto the sum of the dry weight content of the phenol-formaldehyde resoleand the total amount of urea (Ut), and the second amount of urea (U2)used in c) is between 15-52 wt. % of the total amount of urea (Ut); or(iv) the total amount of urea (Ut) is between 42 and 50 wt. % relativeto the sum of the dry weight content of the phenol-formaldehyde resoleand the total amount of urea (Ut), and the second amount of urea (U2)used in c) is between 63% and 66 wt. % of the total amount of urea; or(v) the total amount of urea (Ut) is about 45 wt. % relative to the sumof the dry weight content of the phenol-formaldehyde resole and thetotal amount of urea (Ut), and the second amount of urea (U2) used in c)is about 56 wt. % of the total amount of urea.In the context of the present invention, it is understood that the rangebetween 30 and 35 wt. % also includes 29.6 wt. %, 29.7 wt. %, 29.8 wt. %and 29.9 wt. %. The total amount of urea (Ut) used results from addingthe first amount of urea (U1) used for the prereact formation in step b)and the second amount of urea (U2) used for the formation of theprereact and urea mixture in step c). The inventors have found that whenUt is below 10 wt. %, the emissions of formaldehyde significantlyincrease. On the other hand, Ut values over 60 wt. % result in reducedbinder mechanical properties and high ammonia emissions.

In a particular embodiment the total amount of urea (Ut) is 30-35 wt. %relative to the sum of the dry weight content of the phenol-formaldehyderesole and the total amount of urea (Ut), and U2 is 22-33 wt. %,preferably 25-30 wt. % of the total amount of urea (Ut), or the totalamount of urea (Ut) is 42-50 wt. %, preferably 45-48 wt. % relative tothe sum of the dry weight content of the phenol-formaldehyde resole andthe total amount of urea (Ut), and U2 is 15-50 wt. %, preferably 20-48wt. %, preferably 25-45 wt. %, preferably 30-43 wt. %, preferably 35-40wt. % of the total amount of urea (Ut).

In a preferred embodiment the total amount of urea (Ut) is between 30and 35 wt. %, preferably 33 wt. % relative to the sum of the dry weightcontent of the phenol-formaldehyde resole and the total amount of urea(Ut), and the second amount of urea (U2) used in c) is between 20-35 wt.% of the total amount of urea (Ut). In another preferred embodiment thetotal amount of urea (Ut) is between 42 and 50 wt. %, preferably between43 and 48 wt. % relative to the sum of the dry weight content of thephenol-formaldehyde resole and the total amount of urea (Ut), and thesecond amount of urea (U2) used in c) is between 15 and 52 wt. % of thetotal amount of urea (Ut). In another preferred embodiment the totalamount of urea (Ut) is between 42 and 50 wt. %, preferably between 43and 48 wt. % relative to the sum of the dry weight content of thephenol-formaldehyde resole and the total amount of urea (Ut), and thesecond amount of urea (U2) used in c) is between 63% and 66 wt. %,preferably about 65 wt. % of the total amount of urea (Ut). In anotherpreferred embodiment the total amount of urea (Ut) is about 40 wt. %relative to the sum of the dry weight content of the phenol-formaldehyderesole and the total amount of urea (Ut), and the second amount of urea(U2) used in c) is about 25 wt. % of the total amount of urea (Ut). Inanother preferred embodiment the total amount of urea (Ut) is about 45wt. % relative to the sum of the dry weight content of thephenol-formaldehyde resole and the total amount of urea (Ut), and thesecond amount of urea (U2) used in c) is about 56 wt. % of the totalamount of urea (Ut).

According to certain embodiments, the addition of a resin apart from theaqueous phenol-formaldehyde resole of step a) is excluded. In particularembodiments, the addition of sodium-silicate resins, polyester resins,melamine resins, novolac resins, epoxi resins, polyamide resins,furane-based resins, phosphate resins, or combinations thereof isexcluded.

In particular, the inventors have surprisingly found that when Ut isbetween 30 and 35 wt. % relative to the sum of the dry weight content ofthe phenol-formaldehyde resole and the total amount of urea (Ut), and U2is between 20-35 wt. % of the total amount of urea or when Ut is between42 and 50 wt. % and U2 is between 15 and 52 wt. % or between 63% and 66wt. %, the emissions of formaldehyde in the resulting product aresignificantly reduced.

The inventors surprisingly found that, starting from the same freeformaldehyde content in the phenol-formaldehyde resole, and with thesame total amount of urea used, by the method according to theinvention, mineral wool products are obtained with formaldehydeemissions which are significantly reduced compared with the emissionsmeasured in the case of methods where the same total amount of urea isused solely during the formation of the prereact, i.e. without spliturea additions. Without wanting to be bound by theory, it appears thatthe split urea addition to the resole and the contact of the secondamount of urea (U2) with the prereact shortly before it is applied tothe mineral fibers, modifies the reaction pathways during curing, sothat it results in a higher amount of formaldehyde being irreversiblylocked to the polymeric thermoset network formed during curing.

An additional advantage of the method of the invention is that the firstamount of urea (U1) can be added by the phenol-formaldehyde resolemanufacturer itself, as soon as the condensation reaction for itsproduction is finished, to obtain a prereact with significantly lowerfree formaldehyde than the resole obtained from condensation. Forinstance, the amount of urea used in this premixing step can be selectedso, that it is sufficient to reduce the free formaldehyde content in theprereact to 0.9 wt. % or less related to the dry weight content of theprereact, preferably to 0.2 wt. % or less as measured according to theISO 11402:2004 (KCN method). The prereact, having such an importantlyreduced free formaldehyde content, is less troublesome regardingpotential toxicological and environmental concerns associated toformaldehyde during storage, transport and handling of this material.

Thus, in preferred embodiments of the invention, the first amount ofurea (U1) contacted with the phenol-formaldehyde resole in step b) isselected to be sufficient as to produce a phenol-formaldehyde-ureaprereact with a free formaldehyde content of 0.9 wt. % or less,preferably of 0.2 wt. % or less, as measured according to the ISO11402:2004 (KCN method) and related to the dry weight content of theprereact.

The lower amount of urea used in the premixing step in the method of theinvention, compared with the situation where the same total amount ofurea (Ut) is used but undivided (this is, all of the urea applied in thepremixing step), results in a higher prereact stability. The prereactobtained in preferred embodiments is stable for at least one week,usually even for several weeks. With stable it is meant that theproperties of the prereact which are crucial for its applicability inthe manufacture of mineral wool, are practically not deteriorated duringthis time. Such properties are for example good water dilutability, lowviscosity, absence of precipitates or adequate B-stage gel time, to namethe most important ones.

The comparatively lower amount of urea used in the premixing step in themethod of the invention also opens the way to the use ofphenol-formaldehyde resole with relatively lower contents of freeformaldehyde. It has been reported that an addition of large molarstoichiometric excess of urea in relation to the free formaldehyde inthe resole for the preparation of the prereact, can result introublesome precipitation of phenol-formaldhehyde tetradimer and in thereduction of the stability of the prereact. Due to the relative reducedamount of urea used in the preparation of the prereact in the method ofthe invention, resoles with lower free formaldehyde content, e.g. withfree formaldehyde content of 10 wt. % or less in relation to the dryweight content of the resole, can be used without compromisingunacceptably the stability of the formed prereact.

The invention also concerns the mineral wool products with reducedformaldehyde emissions obtained by the method according to theembodiments described herein, as well as the use of these mineral woolproducts for the insulation of buildings, transportation, air-conductingducts or appliances.

Additionally, certain embodiments of the invention relate to a methodfor the preparation of a phenol-formaldehyde-urea prereact with low freeformaldehyde content, wherein the method comprises providing aphenol-formaldehyde resole having a free formaldehyde content of wt. %or less, preferably of 6 wt. % or less, also preferably of at least 1wt. %, related to the dry weight content of the resole, contacting theresole with a sufficient amount of urea, as to reduce the freeformaldehyde content in the prereact to 0.9 wt. % or less, preferably0.2 wt. % or less, according to ISO 11402:2007 (KCN method) and relatedto the dry weight content of the prereact, and allowing the resole andurea mixture to react, preferably for at least 1 h, more preferably forat least 2 h. Also preferably, the amount of urea in this embodiedmethod for the preparation of a prereact is at least 5 wt. %, morepreferably at least 10 wt. %, and preferably at most 20 wt. %, relatedto the dry weight content of the prereact. In these embodiments, thephenol-formaldehyde resole is preferably substantially free ofnitrogenated compounds (compounds comprising at least one nitrogenatom), particularly substantially free of a compound selected from urea,ammonia, ammonium inorganic or organic salts, alkanolamines, alkylaminesand/or melamine.

DEFINITIONS

By substantially free, along this description, it is meant that theconcentration of the corresponding compound in the resole, prereact orbinder, is sufficiently low as to be negligible. In this context, itshould be understood however that the compound in question might bepresent as traces, e.g. from unintended cross-contamination, preferablyat a concentration of 0.1 wt. % related to the dry weights of theresole, prereact or binder.

In the context of this disclosure, dry weight content is defined as theweight fraction of residue remaining after drying 3 g of the aqueouscomposition (resole, prereact or binder) at 135° C. for 1 hour in aventilated oven, as measured

e.g. according to ISO 3251:2008.

The term binder refers to the aqueous mixture of components which isapplied to the fibers in the manufacture of mineral wool products andsubsequently cured to produce the bonding of the fibers at theircross-over points by the cured binder. The binder is commonly preparedon-site, meaning that the binder is prepared in the mineral woolproduction plant, usually continuously, shortly before it is applied tothe fibers.

By curing it is meant that the material in question undergoes a settingreaction (hardening or crosslinking reaction), e.g. when heated over100° C. in a curing oven (thermosetting).

DETAILED DESCRIPTION OF THE EMBODIMENTS OF THE INVENTION

The aqueous phenol-formaldehyde resole suitable for the method of thepresent invention is a water soluble curable resole having freeformaldehyde, resole which is produced by methylolation and condensationof a phenolic compound with formaldehyde in the presence of an alkalinecatalyst by methods known in the art. In resoles, the molar ratio ofphenol:formaldehyde is <1. Phenol-formaldehyde resoles are reactivemixtures with methylol functional groups, which undergo a self-curingreaction under influence of heat or acids. The resoles are thuspartially reacted thermosets, also known as resins, prepolymers orprecondensates, stable at low temperature and alkaline pH, and which canbe further condensed to a thermoset in a curing reaction by applicationof heat and/or at acidic pH value. The skilled person is aware of howsuch resole is commonly manufactured and recognizes how to modify thedifferent reaction phases and parameters to obtain the characteristicsdescribed in the preferred embodiments of the invention. Such parametersinclude e.g. the phenol:formaldehyde molar ratio, the catalyst type andamount, and the condensation reaction time and temperature.

The phenol:formaldehyde molar ratio for the preparation of the resole ofthe method of the invention is preferably in the range 1:2-1:6. Thestoichiometric excess of formaldehyde assures the predominant formationof low molecular weight species from methylolation and condensation,lower solution viscosity and low free phenol content in the resole. Themolar excess of formaldehyde also has the consequence that free,unreacted, formaldehyde is contained in the aqueous resole afterreaction.

Although for the sake of clarity in this description the suitable resoleis referred to as phenol-formaldehyde resole, it has to be understoodthat it is not implied that the resole might only comprise unsubstitutedphenol and formaldehyde as components. Other components might be presentin the resole without departing from the scope of the invention. Suchcomponents can be for instance substituted phenol derivatives such asalkylphenols, phenol esters, or resorcinol and its derivatives, orformaldehyde related compounds such as paraformaldehyde, or higheraldehydes such as butyraldehyde, acrolein or glyoxal. Other compoundshaving hydroxy or carboxy groups can be also reacted with phenol andformaldehyde, such as carbohydrates or alkanolamines, and even compoundshaving functional groups different than hydroxy or carboxy, such ashexamethylenetetramine, can included in the reaction. It is howeverpreferred that the sum of the weights of unsubstituted phenol andformaldehyde in the resole totals at least 80 wt. %, preferably at least90 wt. %, of the dry weight of the resole.

Advantageously, resoles with low free formaldehyde content, i.e. withfree formaldehyde content of 10 wt. % or less in relation to the dryweight content of the resole, can be used in the method of theinvention. According to certain embodiments of the invention, the freeformaldehyde content in the resole is preferably 10 wt. % or less, morepreferably 6 wt. % or less, also preferably at least 1 wt. %, related tothe dry weight content of the resole, when measured according to themethod ISO 9397:1995 (hydroxylamine hydrochloride method). A centraladvantage of using resole with these levels of free formaldehyde contentin the method of the invention is that mineral wool products obtained byapplying the method of these embodiments are satisfactory in mechanicalperformance, and additionally they have lower emissions of formaldehyde.In particular, sufficiently low free formaldehyde content in the resoleallows the manufacture of mineral wool products with formaldehydeemissions lower than 10 μg/ms, and more preferably lower than 8 μg/ms.The formaldehyde emissions from mineral wool products relate to theemissions when the products are stored in a test chamber with airexchange and under controlled conditions for 28 days and then, theformaldehyde concentration in the air in the chamber is measuredaccording to standard method ISO 16000-3:2011.

According to the method of certain embodiments, the preferredphenol-formaldehyde resole has a dry weight content of 40-60 wt. %. Thecontent of unreacted free phenol in the resole is preferably at most 6wt. %, more preferably at most 2 wt. %, with respect to the resole dryweight content. The water dilutability of the resole in demineralizedwater at 20° C. is suitably greater than 10 parts by weight (this is, atleast 10 g of water can be added to 1 g of resole before permanentturbidity appears), preferably greater than 20 parts, and morepreferably greater than 50 parts. The resole viscosity is preferably atmost 50 mPa·s at 20° C., more preferably at most 30 mPa·s, when measuredfor the resole aqueous solution with 45 wt. % dry weight content. The pHof the resole solution is preferably higher than 8, more preferablyhigher than 8.5, and even more preferably higher than 8.9. The B-Stagegel time of the resole preferably ranges from 2 to 15 minutes at 130° C.The methods used to determine these values are known to the skilledperson, and explained briefly with some level of detail below.

In preferred embodiments, the phenol-formaldehyde resole, before it iscontacted with urea to form the phenol-formaldehyde-urea prereact, has atotal concentration of nitrogen lower than 1.0 wt. %, preferably lowerthan 0.6 wt. %, related to the dry weight content of the resole.Preferably, this resole is substantially free of nitrogenated compounds(compounds comprising at least one nitrogen atom), particularlysubstantially free of a compound selected from urea, ammonia, ammoniuminorganic or organic salts, alkanolamines, alkylamines and/or melamine.

The phenol-formaldehyde resole, according to certain embodiments of theinvention, is substantially free of formaldehyde scavengers selectedfrom the group of amines, tannins, sulfite and bisulfite salts,compounds with methylene active groups, glycine, resorcinol and itsderivatives, alkanolamines, and mixtures thereof.

Resoles with the properties described in preferred embodiments hereinare available from resole manufacturing companies such as MomentivePerformance Materials or Prefere Resins.

The method according to the invention comprises a step(step b)) ofcontacting the phenol-formaldehyde resole with a first amount of urea(U1), and allowing the resole and urea mixture to react, in order toprepare a phenol-formaldehydeurea prereact. The contacting step can bedone by adding the urea (both in solid or liquid form), normally underefficient stirring, to the aqueous resole composition. After the ureaand the resole are contacted, they are vigorously mixed and allowed toreact by leaving the mixture to evolve during at least 1 hour,preferably for at least 2 hours, either in the same reactor used for thepreparation of the resole, or in a separated container. The temperatureduring this step b) including the contacting, the mixing and thereacting phases leading to the prereact formation, ranges between10-100° C., preferably between 15-80° C., preferably between 18-70° C.,preferably between 20-60° C., preferably between 30-50° C., morepreferably between 35-45° C. In a preferred embodiment the temperaturein step b) does not exceed 70° C., more preferably the temperature instep b) is between 20-60° C. Higher temperatures within the range10-100° C. lead to accelerate the condensation reaction so that saidreaction needs to be stopped sooner to avoid advancing the condensationbeyond the desired point. In a preferred embodiment thephenol-formaldehyde resole and first amount of urea (U1) are allowed toreact in step b) of the method of the invention for at least 1 hour at atemperature between 10-60° C. to prepare the prereact.

In preferred embodiments of the invention, the first amount of urea (U1)contacted with the phenol-formaldehyde resole in step b) is selected tobe sufficient as to produce a phenol-formaldehyde-urea prereact with afree formaldehyde content of 0.9 wt. % or less related to the dry weightcontent of the prereact, preferably of 0.2 wt. % or less, as measuredaccording to the ISO 11402:2004 (KCN method).

The first amount of urea (U1) preferably ranges from 34-85 wt. %, forexample 44 wt. %, preferably from 48-85 wt. %, preferably from 65 to 80wt. %, for example 75 wt. %, related to the total amount of urea (Ut).

Particularly good results of prereact stability, low free formaldehydeprereact content and low formaldehyde emissions have been achieved whenusing a resole with free formaldehyde content of less than 6 wt. %related to the dry weight content of the resole, contacted with a firstamount of urea (U1) of at least 34 wt. %, more preferably at least 48wt. %, more preferably at least 65 wt. %, relative to the total amountof urea (Ut).

In a subsequent step c), the phenol-formaldehyde-urea prereact formed instep b) is contacted with a second amount of urea (U2) to produce amixture of prereact and urea. The start point of this step c) isseparated in time from the end of step b), preferably at least for 24hours, and more preferably at least for 72 hours. This step c) willusually be done by the mineral wool manufacturer at its facilities,shortly before the prereact and urea mixture is applied to the mineralfibers in the manufacture of mineral wool products. In contrast withthis, the preparation of the phenol-formaldehyde-urea prereact willusually be done by the resole producer, who delivers the finishedprereact to the mineral wool manufacturer.

In step c), the phenol-formaldehyde-urea prereact and the second amountof urea (U2) can be contacted and well mixed in a container adapted forthis purpose, or alternatively, and currently less preferred, thecontacting/mixing can be done continuously “in-line” in the mineral woolmanufacturing line, as the mixture is transported to the binderapplication station. The prereact and second amount of urea (U2) mixtureis preferably kept at a temperature lower than 50° C., preferably lowerthan 40° C., more preferably under 30° C. at all time, and morepreferably between 20-25° C. until it is applied onto the surface of themineral fibers, to avoid premature advance of the condensation reaction.

The phenol-formaldehyde-urea prereact and the second amount of urea (U2)are contacted and mixed shortly before the resulting mixture is appliedto the surface of mineral fibers, preferably less than 48 h before, andmore preferably less than 24 h before.

The method according to the invention foresees that the total amount ofurea (Ut), this is, the sum of the first (U1) and second (U2) amounts ofurea used in steps b) and c), relative to the sum of the dry weight ofthe phenol-formaldehyde resole and the total amount of urea(Ut), and thesecond amount of urea (U2), are used in the following ranges:

(i) when the total amount of urea (Ut) is between 30 and 35 wt. %relative to the sum of the dry weight content of the phenol-formaldehyderesole and the total amount of urea (Ut), the second amount of urea (U2)used in c) is between 20-35 wt. % of the total amount of urea (Ut); or(ii) when the total amount of urea (Ut) is about 40 wt. % relative tothe sum of the dry weight content of the phenol-formaldehyde resole andthe total amount of urea (Ut), the second amount of urea (U2) used in c)is about 25 wt. % of the total amount of urea; or(iii) when the total amount of urea (Ut) is between 42 and 50 wt. %relative to the sum of the dry weight content of the phenol-formaldehyderesole and the total amount of urea (Ut), the second amount of urea (U2)used in c) is between 15-52 wt. % of the total amount of urea (Ut); or(iv) when the total amount of urea (Ut) is between 42 and 50 wt. %relative to the sum of the dry weight content of the phenol-formaldehyderesole and the total amount of urea (Ut), the second amount of urea (U2)used in c) is between 63% and 66 wt. % of the total amount of urea; or(v) when the total amount of urea (Ut) is about 45 wt. % relative to thesum of the dry weight content of the phenol-formaldehyde resole and thetotal amount of urea (Ut), the second amount of urea (U2) used in c) isabout 56 wt. % of the total amount of urea. The inventors surprisinglyfound that when this combination of features is used, the emissions offormaldehyde from the mineral wool products manufactured issignificantly reduced compared with the case where the same total amountof urea is only used in the preparation of the prereact (without “cold”urea addition).

In order to manufacture mineral wool products according to the method ofthe invention, in a further step d), the mixture ofphenol-formaldehyde-urea prereact and second amount of urea (U2) fromstep c) is applied to the surface of mineral fibers. The mixture ofprereact and second amount urea (U2) is applied to the fibers as part ofa binder. The binder optionally comprises additives employed either toassist in the manufacture of mineral wool products or to improve themineral wool product properties. The binder is preferably an aqueouscomposition with a non-aqueous content in the range 4-15 wt. %, relativeto the aqueous binder weight.

The optional additives comprised in the binder, in addition to thephenol-formaldehyde-urea prereact and the second amount of urea (U2),are preferably in a concentration of more than 1 wt. % and less than 30wt. % related to the non-aqueous content of the binder, more preferablyin a concentration of 5-25 wt. %, more preferably in a concentration of10-20 wt. %, even more preferably in a concentration of 15-18 wt. %. Theoptional additives include at least one additive selected from thefollowing groups of substances: i) curing catalysts, such as ammoniumsulfate; ii) resin extenders different than urea, such as carbohydrates;iii) anti-dust agents such as mineral oil; iv) adhesion promoters suchas silanes; and v) water repellent agents such as silicones, and moreparticularly reactive silicones. It is particularly preferred to includeup to 10 wt. % of molasses and/or glucose as resin extender.

In certain embodiments, resins are excluded from the optional additives.In particular embodiments, the addition of sodium-silicate resins,polyester resins, melamine resins, novolac resins, epoxi resins,polyamide resins, furane-based resins, phosphate resins, or combinationsthereof is excluded.

In preferred embodiments, the mixture of phenol-formaldehyde-ureaprereact and second amount of urea (U2) will be largely diluted withfresh or process water, and optionally mixed with the additives in orderto prepare the binder. Wherein no additives are used, the binder mightcomprise only the prereact and second amount of urea (U2) mixture,preferably diluted with water to the desired concentration.

The concentration of the different components in the binder preferablyranges from 40-90 wt. % of phenol-formaldehyde resole, 30-50 wt. % totalurea (sum of first (U1) and second (U2) amounts of urea) and 1-20 wt. %of additives, based on the non-aqueous weight of the binder.

In preferred embodiments, the mixture of the phenol-formaldehyde-ureaprereact and the second amount of urea (U2) is applied in atomized formto the attenuated individual fine mineral fibers being produced by afiberizer from a hot molten mineral mixture. The atomization can beproduced by spraying nozzles or similar devices oriented in a directionso that the sprayed mixture meets the surface of the attenuated fibers.The mixture contacts the surface of the mineral fibers when they arestill warm. The impregnated fibers are collected on a foraminousconveyor in a forming chamber, where a primary uncured mat is formed. Asignificant part of the water comprised in the binder is evaporated atthis stage.

Next, the primary mat is densified and transported by a series ofconveyors to a heated curing oven. The binder is then cured attemperatures above 100° C., preferably at a temperature between 140-180°C., more preferably between 150-170° C., even more preferably between155-165° C. The curing time preferably ranges from 2-5 min. The curedmineral wool mat is afterwards trimmed and shaped into its finaldimensions, optionally rolled up, and packaged.

In certain embodiments, the phenol-formaldehyde-urea prereact and secondamount of urea (U2) mixture is applied as part of a binder to the fibersin an amount to produce a content of solid binder related to the weightof the mineral fibers in the final mineral wool product after curingbetween 1.5 wt. % and 15 wt. %, preferably between 3 and 12 wt. %, evenmore preferably between 5 and 10 wt. %. The amount of cured binderrelative to the mineral fiber weight in the mineral wool product ismeasured as LOI (loss on ignition) according to ISO 29771:2008.Thus, ina preferred embodiment the mineral wool product obtained by the methodof the invention has a LOI of between 1.5 wt. % and 15 wt. %.

It has been found that when the phenol-formaldehyde resole has a freeformaldehyde content lower than 6 wt. % related to the dry weightcontent of the resole, the second amount of urea (U2) ranges from 20-35wt. % related to the total amount of urea (Ut); and the total amount ofurea (Ut) adds up to 30-35 wt. % related to the sum of the dry weight ofthe resole and the total weight amount of urea (Ut), or when the secondamount of urea (U2) ranges from 63-66 wt. % related to the total amountof urea (Ut); and the total amount of urea (Ut) adds up to 42-50 wt. %related to the sum of the dry weight of the resole and the total weightamount of urea (Ut), and without the need of using further formaldehydescavengers, the mineral wool products manufactured according to thisembodiment of the method of the invention, surprisingly exhibitformaldehyde emissions lower than 10 μg/ms, and even lower than 8 μg/ms,when measured according to ISO 16000-3:2011. Thus, in one aspect thepresent invention relates to a mineral wool product with formaldehydeemissions lower than 10 μg/ms obtained by the method of the invention,preferably with formaldehyde emissions lower than lower than 8 μg/mswhen measured according to ISO 16000-3:2011. In a preferred embodiment,the mineral wool product obtained by the method of the invention furtherhas a LOI of between 1.5 wt. % and 15 wt. %. The mineral wool productobtained by the method of the invention exhibits a non-acidic behaviorin pH terms, namely when said mineral product is in contact with water,said water does not acquire an acid pH.

TESTING METHODS

The free formaldehyde content of the resole is measured for instanceaccording to the international standard ISO 9397:1995, using thehydroxylamine hydrochloride procedure. This method involves thefollowing general principle: The formaldehyde present in the resole isconverted to the oxime with hydroxylamine hydrochloride. Then thehydrochloric acid formed during this reaction is determined bypotentiometric back-titration, using a sodium hydroxide solution. Thefree formaldehyde content of the resole with respect to its dry contentis then calculated from the amount of sodium hydroxide.

The free formaldehyde content of the phenol-formaldehyde-urea prereactis measured according to ISO 11402:2004, using the KCN method.Alternative methods for measuring the free formaldehyde content are HPLCor NMR.

The free or unreacted phenol content of the resole is measured forinstance according to the international standard ISO 8974:2002. Thisinternational standard determines the free phenol content by gaschromatography using either a weighed amount of internal standard beingadded to the test portion or using a stock solution of internalstandard. The internal standard used is 1-octanol. The free phenolcontent of the resole is then calculated with respect to its dry weightcontent.

The content of nitrogen in the phenol-formaldehyde resole is measuredfor instance with the Kjeldahl method.

The resole water dilutability (or miscibility) is measured withdemineralized water and at 20° C. according to the internationalstandard ISO 8989:1995 method. Resole dilutability is a measure of themass of demineralized water relative to the mass of aqueous resole whichresults in permanent turbidity in the liquid resole. This methodinvolves adding water to the resole until turbidity persists for aminimum of 30 seconds after agitation.

The viscosity of the resole is measured at 20° C. using a Brookfieldviscometer, for example with the spindle 1 and r.p.m. The viscosity asreferred to in the present invention is based on an aqueous resolehaving a dry weight content of 45 wt. %.

The B-Stage gel-time of the resole is measured at 130° C. according tothe international standard ISO 8987:2005.

The content of cured binder in the mineral wool product (LOI) ismeasured according to the international standard ISO 29771:2008.

The amount of formaldehyde emissions from mineral wool products ismeasured from freshly manufactured samples, for instance, according toISO 16000-3:2011. The method involves placing the fresh samples into a212 1 acclimatized glass chamber equipped with a ventilator and set at atemperature 23±1° C., a relative humidity of 50±5%, air flow 0.2±0.1 m/sand an air exchange rate 0.5 h-1±5% for 28 days. Other settings are theloading factor of 1 m² of sample surface per m³ of test chamber volume,and a specific area air exchange rate of 0.5 m³/m² h. Emittedformaldehyde is determined in μg/ms from air samples of the air in thechamber taken on to adsorbent cartridges coated with2,4-dinitrophenylhydrazine (DNPH) at the time of the measurement (after28 days in this case) and the hydrazones formed are subsequentlyanalyzed by high performance liquid chromatography (HPLC) with detectionby ultraviolet absorption.

EXAMPLES

A phenol-formaldehyde resole characterized by having a pH 9,6, viscosity20 mPa·s, dilutability in demineralized water >50, B-Stage gel-time of 3min, 45 wt. % dry weight content supplied by a commercial provider, wasemployed for the manufacture of glass wool products. This resole wasfurther characterized by a phenol content under 2 wt. %, nitrogencontent <0.6 wt. %, and free formaldehyde content of 6 wt. %, all wt. %based on the resole dry weight content.

In inventive examples, two amounts of urea U1 and U2 were added to thephenol-formaldehyde resole in two separated steps. The first amount U1was used to prepare a phenol-formaldehyde-urea prereact, and it wasadded to the same reactor where the resole had been prepared, once thecondensation reaction was quenched. The mixture was allowed to react forseveral hours in the same reactor. One week later, the second amount ofurea U2 was added to the prereact and mixed under agitation at approx.25° C. for 1 hour, before it was employed for the manufacture of glasswool products.

A binder mixture was prepared by mixing the resulting mixture ofprereact and second amount of urea U2, with water, ammonium sulfate,mineral oil and aminopropyltrimethoxysilane. The binder was applied tothe surface of glass wool fibers, in form of small drops, by sprayingrings, as the fibers from a disc fiberizer, attenuated by hot airblowers, fell down to a foraminous conveyor belt. The glass fibersbearing the binder were collected in the form of an uncured mat,densified and transported to a curing oven, where the binder was heatedto a temperature between 140-180° C. for 3-5 minutes to produce itscuring. After curing, the produced glass wool mat had a density of 29.5kg/m3 and a thickness of 100 mm. The cured binder content measured asLOI was 6.5 wt. % related to the weight of the fibers.

In the comparative example, the same procedure was repeated, except thatall the urea was added undivided, in one single step, for the formationof the prereact, and that no urea was subsequently added to theprereact.

Table 1 depicts the amounts of urea U1 and U2 as weight percentagesrelative to the total amount of urea, in inventive and comparativeexamples, as well as the results obtained of formaldehyde emissionsafter 28 days from the glass wool products manufactured.

TABLE 1 U1 First U2 Second Formaldehyde Urea amount of Urea amount ofurea emissions Total (wt. % of Ut) (wt. % of Ut) (μg/m³) Example 1 45%66% 33% 7 PFU30 + U15 Example 2 35% 71% 29% 7 PFU25 + U10 Example 3: 45%33% 66% 6 PFU15 + U30 Example 4: 30% 66% 33% 9 PFU20 + U10 Example 5:40% 75% 25% 8 PFU20 + U10 Example 6: 45% 44% 56% 7 PFU20 + U10Comparative 30% 100%   0% 12 Example (PFU30)

The phenol-formaldehyde-urea prereact of examples 1 to 6 had a freeformaldehyde content of <0.2 wt. % related to the dry weight of theprereact.

1-16. (canceled)
 17. A method for the manufacture of mineral woolcomprising the steps of: a) providing an aqueous phenol-formaldehyderesole with free formaldehyde, b) preparing a phenol-formaldehyde-ureaprereact by contacting the resole with a first amount of urea andallowing the mixture to react; c) contacting the prereact with a secondamount of urea, d) applying the resulting mixture of prereact and secondamount of urea, as part of a binder, to the surface of mineral fibers;and e) curing the binder on the surface of the mineral fibers; whereinthe total amount of urea is between 30 and 35 wt. % relative to the sumof the dry weight content of the phenol-formaldehyde resole and thetotal amount of urea, and the second amount of urea used in c) isbetween 20-35 wt. % of the total amount of urea.
 18. The methodaccording to claim 17, wherein the total amount of urea is 30-35 wt. %relative to the sum of the dry weight content of the phenol-formaldehyderesole and the total amount of urea, and U2 is 22-33 wt. %, preferably25-30 wt. % of the total amount of urea.
 19. The method according toclaim 17, wherein the total amount of urea is between 30 and 35 wt. %relative to the sum of the dry weight content of the phenol-formaldehyderesole and the total amount of urea, and the second amount of urea usedin c) is between 20-35 wt. % of the total amount of urea.
 20. The methodaccording to claim 17, provided that the addition of a resin apart fromthe aqueous phenol-formaldehyde resole of step a) is excluded.
 21. Themethod according to claim 17, wherein the phenol-formaldehyde resole instep a) has a free formaldehyde content at most 10 wt. % related to thedry weight content of the resole, preferably at most 6 wt. %.
 22. Themethod according to claim 17, wherein the phenol-formaldehyde resole hasa water dilutability at 20° C. greater than 10 parts by weight, aviscosity of at most 50 mPa·s at 20° C. and 45 wt. % dry weight content,a pH higher than 8, and a B-stage gel time ranging from 2-15 minutes at130° C.
 23. The method according to claim 17, wherein in step b), thephenol-formaldehyde resole and first amount of urea (U1) are allowed toreact for at least 1 hour, preferably at a temperature between 10-60° C.to prepare the prereact.
 24. The method according to claim 17, whereinin step c), the second amount of urea (U2) is added to the prereact atleast 24 hours, preferably at least 72 hours, after the prereact hasbeen formed.
 25. The method according to claim 17, wherein the prereactand second amount of urea (U2) are contacted in step c) less than 48hours before this mixture is applied to the surface of the fibers instep d).
 26. The method according to claim 17, wherein in step d), themixture of prereact and second amount of urea(U2) is applied to themineral fibers as part of a binder comprising additives in aconcentration of 1-30 wt. % related to the non-aqueous content of thebinder.
 27. The method according to claim 17, wherein the first amountof urea (U1) in step b) is selected to produce a prereact with a freeformaldehyde content of 0.9 wt. % or less, preferably of 0.2 wt. % orless, related to the dry weight content of the prereact.
 28. The methodaccording to claim 17, wherein the phenol-formaldehyde resole in step a)has a total concentration of nitrogen lower than 1.0 wt. %, preferablylower than 0.6 wt. %, related to the dry weight content of the resole.29. The method according to claim 17, wherein the phenol-formaldehyderesole in step b) is substantially free of formaldehyde scavengersselected from the group of amines, tannins, sulfite and bisulfite salts,compounds with methylene active groups, glycine, resorcinol and itsderivatives, alkanolamines, and mixtures thereof
 30. A mineral woolproduct obtained by the method of claim 17, wherein the emissions offormaldehyde of said mineral wool product are lower than 10 μg/m³,preferably lower than 8 μg/m³measured according to ISO 16000-3:2011. 31.The mineral wool product according to claim 30, wherein the mineral woolproduct further has a LOI of between 1.5 and 15 wt. %.
 32. The use ofthe mineral wool product according to claim 30 for the insulation ofbuildings, transportation, airconducting ducts and/or appliances.
 33. Amethod for the manufacture of mineral wool comprising the steps of: a)providing an aqueous phenol-formaldehyde resole with free formaldehyde,b) preparing a phenol-formaldehyde-urea prereact by contacting theresole with a first amount of urea and allowing the mixture to react; c)contacting the prereact with a second amount of urea, d) applying theresulting mixture of prereact and second amount of urea, as part of abinder, to the surface of mineral fibers; and e) curing the binder onthe surface of the mineral fibers; wherein the total amount of urea isabout 40 wt. % relative to the sum of the dry weight content of thephenol-formaldehyde resole and the total amount of urea, and the secondamount of urea used in c) is about 25 wt. % of the total amount of urea.34. A method for the manufacture of mineral wool comprising the stepsof: a) providing an aqueous phenol-formaldehyde resole with freeformaldehyde, b) preparing a phenol-formaldehyde-urea prereact bycontacting the resole with a first amount of urea and allowing themixture to react; c) contacting the prereact with a second amount ofurea, d) applying the resulting mixture of prereact and second amount ofurea, as part of a binder, to the surface of mineral fibers; and e)curing the binder on the surface of the mineral fibers; wherein thetotal amount of urea is between 42 and 50 wt. % relative to the sum ofthe dry weight content of the phenol-formaldehyde resole and the totalamount of urea, and the second amount of urea used in c) is between15-52 wt. % of the total amount of urea.
 35. The method according toclaim 33, wherein the total amount of urea is 42-50 wt. %, preferably45-48 wt. % relative to the sum of the dry weight content of thephenol-formaldehyde resole and the total amount of urea, and U2 is 15-50wt. %, of the total amount of urea.
 36. The method according to claim33, wherein the total amount of urea is between 42 and 50 wt. % relativeto the sum of the dry weight content of the phenol-formaldehyde resoleand the total amount of urea and the second amount of urea used in c) isbetween 63% and 66 wt. % of the total amount of urea.
 37. A method forthe manufacture of mineral wool comprising the steps of: a) providing anaqueous phenol-formaldehyde resole with free formaldehyde, b) preparinga phenol-formaldehyde-urea prereact by contacting the resole with afirst amount of urea and allowing the mixture to react; c) contactingthe prereact with a second amount of urea, d) applying the resultingmixture of prereact and second amount of urea, as part of a binder, tothe surface of mineral fibers; and e) curing the binder on the surfaceof the mineral fibers; wherein the total amount of urea is between 42and 50 wt. % relative to the sum of the dry weight content of thephenol-formaldehyde resole and the total amount of urea, and the secondamount of urea used in c) is between 63% and 66 wt. % of the totalamount of urea.
 38. A method for the manufacture of mineral woolcomprising the steps of: a) providing an aqueous phenol-formaldehyderesole with free formaldehyde, b) preparing a phenol-formaldehyde-ureaprereact by contacting the resole with a first amount of urea andallowing the mixture to react; c) contacting the prereact with a secondamount of urea, d) applying the resulting mixture of prereact and secondamount of urea, as part of a binder, to the surface of mineral fibers;and e) curing the binder on the surface of the mineral fibers; whereinthe total amount of urea is about 45 wt. % relative to the sum of thedry weight content of the phenol-formaldehyde resole and the totalamount of urea, and the second amount of urea used in c) is about 56 wt.% of the total amount of urea.